Rechargeable lithium battery technology has become increasingly important in recent years because it is providing new, lightweight, high energy density batteries for powering applications in the rapidly growing electronics industry. These batteries are also of interest because of their possible application in electric vehicles and hybrid electric vehicles.
State-of-the-art rechargeable lithium batteries are known as “lithium-ion” batteries because during charge and discharge, lithium ions are shuttled between two host electrode structures with a concomitant reduction and oxidation of the host electrodes. Lithium batteries are prepared from one or more lithium electrochemical cells comprising positive and negative electrodes and an electrolyte. Such electrodes are usually tested, before insertion in lithium-ion battery, in lithium metal batteries which include as an anode (negative electrode), a metallic lithium-based material (used as a reference with a potential of 0V), as a cathode (positive electrode), for example a transition metal oxide, and an electrolyte interposed between electrically insulated, spaced-apart, positive and negative electrodes. The electrolyte typically comprises a salt of lithium dissolved in one or more solvents, typically nonaqueous (aprotic) organic solvents. By convention, during discharge of the cell, the negative electrode of the cell is defined as the anode. During use of the cell, lithium ions (Li+) are transferred to the negative electrode on charging. During discharge, lithium ions (Li+) are transferred from the negative electrode (anode) to the positive electrode (cathode). Upon subsequent charge and discharge, the lithium ions (Li+) are transported between the electrodes. Cells having metallic lithium anode and transition metal oxide cathode are charged in an initial condition. During discharge, lithium ions from the metallic anode pass through the liquid electrolyte to the electrochemically active material of the cathode whereupon electrical energy is released. During charging, the flow of lithium ions is reversed and they are transferred from the positive electrode active material through the ion conducting electrolyte and then back to the lithium negative electrode.
The best known lithium-ion cell is a 3.5 V LixC6/Li1−xCoO2 cell, in which lithium is extracted from a layered LiCoO2 structure (positive electrode or cathode) during charge and inserted into a carbonaceous structure (negative electrode or anode), typically graphite or a “hard” or pyrolyzed carbon, presenting a specific capacity around 372 mAh/g. Lithiated carbons can approach and reach the potential of metallic lithium at the top of the charge cycle. Therefore, these negative electrodes or anodes are highly reactive materials, particularly in the presence of a highly oxidizing Li1−xCoO2 positive electrode and a flammable organic electrolyte. There is, therefore, a concern about the safety of charged lithium-ion cells; sophisticated electronic circuitry has to be incorporated into each cell to protect them from overcharge and abuse. This invention addresses the need to find alternative negative electrode materials to carbon.
Negative electrodes different from carbon ones have been already described, such as tin oxide, tin or antimony alloys. But, these electrodes present a relatively poor capacity and a high variation of expansion/contraction volume during insertion/desinsertion of lithium (around 400% by volume) which induces a rapid decay in mechanical properties. Their low potential may also raise safety issues, as the carbon.